This invention relates to an improved structure of the electrode portion in a semiconductor possessing a current blocking layer.
As current confinement means in a semiconductor device, it is known to form a confinement current passing part in a size suited to the current passage in an insulation film of SiO.sub.2, SiN.sub.x or the like, and to evaporate an electrode metal layer thereon.
As its practical example, one as shown in FIG. 7 has been already presented.
In the semiconductor laser device in FIG. 7, an n-type layer 2, InGaAsP active layer 3, p-type layer 4, and InGaAsP contact layer 5 are sequentially grown on the upper surface of an n-type InP substrate 1, and an SiO.sub.2 insulation film 6 is evaporated on the InGaAsP contact layer 5, and a part of the SiO.sub.2 insulation film 6 is removed in a window form by etching means so as to expose the surface of the InGaAsP contact layer 5, thereby forming a confinement current passing part 9, and then a p-type electrode metal layer 7 is evaporated on the surface of InGaAsP contact layer 5 and on the SiO.sub.2 insulation film 6, and an n-type electrode metal layer 8 is evaporated on the lower surface of the n-type InP substrate 1.
In the case of thus fabricated semiconductor laser device, by applying a voltage between the p-type electrode metal layer 7 and the n-type electrode metal layer 8, the current passes only through the confinement current passing part 9 disposed on the SiO.sub.2 insulation film 6 and flows to the side of n-type electrode metal layer 8, and this current emits light when passing through the InGaAsP active layer 3.
This light emitting portion is nearly equal to or larger than the confinement current passing part 9.
In such prior art, however, the following technical problems are left unsolved.
That is, the coefficient of thermal expansion of insulation film 6 of SiO.sub.2, SiN.sub.x or the like is smaller by one or two digits than the coefficient of thermal expansion of a compound semiconductor, and along with the temperature rise when injecting current, the stress is concentrated on the end portion of the dielectric film 6, and a defect occurs in the contact layer 5.
This defect propagates up to the active layer 3 along the crystal direction of the semiconductor crystal, and deteriorates the light emission efficiency of the semiconductor laser device.